The Research Of The Influence To Rheological Properties Of Poplars Under Microwave Pretreatment

The paper closely combined with the national natural science fund project,taking poplar wood as the object and using the microwave technology to pretreatment poplar wood,observing the macroscopic changes and microcosmic changes of the poplar wood.The mechanical properties of poplar were discussed after processed by microwave.On these basis,the flexural creep properties of poplar were tested with different microwave pretreatment conditions and different loads.According to the rheological theory,the experimental curves were fitted and analyzed by Burgers rheological model.At the same time,the Burgers rheological model was improved to fit the experimental curves and predictive creep curves better.The main innovative conclusions showed as follows:(1)From a macroscopic point of view,there was only a layer of water vapor on the specimen surface when the microwave pretreatment got lower intensity.Some of the specimen surfaces were cracked obviously and broken directly with higher microwave pretreatment intensity.From the microcosmic point of view,the holes and hole cytoderm of untreated poplar internal structure were smoothly and not broken.The cross sections and lengthwise section of poplar with microwave pretreatment were more roughly and the coarse of hole-edge were more gracile to become a network structure.Some holes were broken and linked to other holes to become a new one which bigger and more anomalous,that even run through the whole cross section and lengthwise section of poplar wood.After the mechanical experiment,the direction of poplar wood holes showed anisotropy of the materials more obviously.(2)The influence of microwave pretreatment to poplar mechanical properties were changed with microwave radiation intensity and irradiating time.When the radiation intensity below 5kW and irradiating time less than 50s,the mechanical properties of poplar reduced slightly,the decrease range was from 8%to 13%.However,when the microwave radiation intensity gets higher or irradiating time gets longer,the elastic modulus of bending and bending strength of poplar have been improved.The elastic modulus of bending has been increased remarkably as strength attains to 18kW,the range reached to 52.6%and the bending strength increased by approximately 20%.(3)The creep curve of poplar under different microwave pretreatment conditions and different loads abided by the similar rule.The slow creep stage and stable creep stage all appeared in the curve.But,there were no third creep stage(accelerate creep stage)showing up.There was a huge difference of the creep increment when change the loads.The instant amount of elastic deformation and the total amount of creep were increased with the increase of loads.There was a different influence on the creep properties of poplar wood under microwave radiation intensity and irradiating time.With the same microwave radiation intensity and different irradiating time,the total amount of creep of each group with 50%breaking strength had increased than that of the each group with 30%breaking strength at the end of the test,the increase rage was from 25%to 69%.With the same microwave irradiating time and different radiation intensity,the total amount of creep of each group with 50%breaking strength had increased above 46%than that of the each group with 30%breaking strength at the end of the test.Under the microwave pretreatment conditions of 65s,15kW,the range reached to 100.3%,which was far more than the biggest increase with the different irradiating time.The deciding coefficient R2 between the simulated curve of Burgers rheological model parameters solved by Origin software and the test curve were above 0.99,which revealed that Burgers rheological model can used to simulate the early stage of creep of poplar,but not to the long-term stage of creep of poplar as the forecast data are too linear and unconformity with reality.Introducing a parameter? based on the Burgers rheological model can commendably solve the problem and the new Burgers rheological model can simulate the early stage of the creep better.The results above can offer some basic data for rheological properties research of poplar with microwave pretreatment,and also provided theoretical and experimental basis for the design of timber to avoid failure of structure caused by huge creep deformation.